Conventionally, polyolefinic resins have in general many advantages such as good productivity, excellent moldability in accordance with various molding techniques, light weight, anti-rust property, impact resistance and the like, and thus have been used in a wide range of applications such as interior or exterior decorations for automobiles, ships or the like, materials for domestic appliances, furniture, miscellaneous goods and construction, and the like.
Since such molded products of polyolefinic resins are generally non-polar as well as crystalline, unlike those polar synthetic resins represented by polyurethane resins, polyamide resins, acrylic resins and polyester resins, it is extremely difficult to perform coating or adhesion to these polyolefinic resins using a general-purpose resin composition.
For this reason, when coating or adhesion is carried out onto a polyolefinic resin molded product, it has been traditional to enhance adherence onto the product surface by treating the surface with a primer or by activating the surface. For example, in the case of an automobile bumper, desired coating or adhesion has been carried out after enhancing adhesiveness to the coating film by subjecting the bumper surface to etching with a halogen-based organic solvent such as trichloroethane, or after subjecting the bumper to pretreatment such as corona discharge treatment, plasma treatment and ozone treatment.
However, coating or adhesion using such conventionally known general-purpose resin compositions requires not only high facility costs but also a long operation time. Also, the finishing cannot be done uniformly and consistently, thus it being liable to cause variations in the state of surface treatment.
Hence, in the past, for example, a composition comprising polyolefin incorporated with maleic acid (JP-B No. 62-21027, etc.), or a composition comprising polyolefin modified by chlorination as the main component (JP-B No. 50-10916, etc.) has been suggested as a coating composition having an improvement in the above-described problems. However, although these compositions have excellent adhesiveness to the polyolefinic molded product, etc., since they have poor weather resistance, their use has been usually limited to the use as a primer or to the applications where weather resistance is not required. Therefore, in the case of performing coating with such compositions in applications where weather resistance is required, typically two-coat finish involving complicated operations is needed.
For this reason, development of a coating material which allows one-coat finish treatment, and which can exhibit excellent adhesiveness to materials even without any pretreatment and has excellent weather resistance, is in progress, and in this pertinent art, there have been suggested, for example, a resin which is obtained by copolymerization of an acrylic monomer and a chlorinated polyolefin (JP-A No. 58-71966, etc.); a coating composition comprising a copolymer of a hydroxyl-containing acrylic monomer and a chlorinated polyolefin, and an isocyanate compound (JP-A No. 59-27968); and the like. However, since these materials contain chlorine, their effect on the environment has become a matter of concern.
There have been also suggested a method of introducing unsaturated bonds to a polyolefin (JP-A No. 1-123812, JP-A No. 2-269109, etc.), a method of introducing organic peroxide (JP-A No. 1-131220, etc.), a method of using bifunctional organic peroxide (JP-A No. 64-36614, etc.) and the like, and these are the means to improve reactivity of polyolefin with radically polymerizable unsaturated monomers.
However, in many cases of the above-described resin compositions and methods for preparation thereof, drawbacks are found such that reaction should be carried out at dilute concentrations, particularly because of the viscosity problem; the efficiency of graft copolymerization to polyolefin is low; since there is a tendency that homopolymers of radically polymerizable unsaturated monomers are generated, the resulting resin solutions are highly liable to undergo separation and cannot be used directly as such, in general; and the coating obtained from these resin solutions has surface tackiness.
Moreover, with regard to adhesion between polyolefin and metal such as aluminum, resin dispersions of modified polypropylene (JP-A No. 63-12651, etc.) have been suggested. However, since these dispersions employ raw materials having high melting points in order to reduce tackiness of the coating film, they have a drawback that the heat-sealing temperature is high.    [Patent Document 1] JP-B No. 62-21027    [Patent Document 2] JP-B No. 50-10916    [Patent Document 3] JP-A No. 58-71966    [Patent Document 4] JP-A No. 59-27968    [Patent Document 5] JP-A No. 1-123812    [Patent Document 6] JP-A No. 2-269109    [Patent Document 7] JP-A No. 1-131220    [Patent Document 8] JP-A No. 64-36614    [Patent Document 9] JP-A No. 63-12651
The present invention is to provide a solvent dispersion of a composite resin which solves the above-described problems of the prior arts.
That is, it is an object of the invention to provide a coating material, a primer, an adhesive, an additive, a binder, a film, and a primer for strippable paints and traffic paints, which can be applied by spray coating as the resin solution does not undergo separation; which show no film surface tackiness when applied to form a coating film; which result in a coating film obtained by using a curing agent having an isocyanate group in the molecule, which exhibits superior weather resistance as compared with coating films of polyolefins modified by chlorination; which result in coating films that exhibit excellent adhesiveness to untreated polyolefinic resin films, sheets or molded products; and which have excellent heat-sealability at low temperatures.